Stacker (or stacking) wheels are commonly used in automated teller machines (ATMs) to stack multiple currency notes prior to dispensing the stack of notes to a user of the ATM. The operation of a stacker wheel can be described with reference to FIG. 1 which shows a schematic side elevation view of a cash dispenser unit 73 of an ATM. The cash dispenser unit 73 includes a stacker wheel assembly 75. The stacker wheel assembly 75 comprises a plurality of stacker wheels 76 spaced apart in a parallel relationship along a shaft 77, each stacker wheel 76 having a plurality of curved tines 78.
FIGS. 2A and 2B show more detailed diagrams of a stacker wheel 201 comprising a plurality of curved tines 202 on a central hub 203. At the centre of the hub 203 is an aperture 204 that enables the stacker wheel 201 to be mounted on a metal shaft (not shown). Currency notes can be held by the stacker wheel in compartments 205 formed between adjacent tines. The width of the stacker wheel is very narrow (2.54 mm) compared to the diameter of the wheel (101.60 mm).
The cash dispenser unit 73 (as shown in FIG. 1) holds a number of currency cassettes 89 each holding a stack of currency notes 68. When one or more notes are to be dispensed from a particular cassette, the pick mechanism 74 associated with the cassette draws a note from the cassette such that its leading edge is gripped between drive rollers 90. The note is then fed along the feed path 72 by further drive rollers 92, through a retard mechanism 10 to the stacker wheel assembly 75. In operation, the stacker wheel assembly 75 rotates continuously in a counter-clockwise direction (for the arrangement shown in FIG. 1) and the note is fed into a compartment 81 formed between adjacent tines 78. If more than one note is to be dispensed, each note is fed into a successive compartment 81 as the stacker wheel assembly 75 rotates. Having completed half a rotation, the note is removed from the stacker wheel assembly 75 by fingers 94 of a stripper plate assembly 96 pivotally mounted on a shaft 98. Once removed from the stacker wheel, the note is placed on a belt 100 resting against the stripper plate assembly 96 and any subsequent notes which are to be dispensed simultaneously with the first note are placed on top of the first note to form a bundle 68′. When the required amount of notes (which may be just one note) have been assembled into the bundle 68′, a pair of belts 102 (only one of which is shown in FIG. 1) is rotated on a shaft 104 such that the bundle 68′ is trapped between the belts 100, 102. The bundle is then fed between belts 100, 102, 106, 108 through a note exit slot 110 in the housing 112 of the cash dispenser unit 73 to a position where the bundle 68′ can be collected by the user of the ATM. If a multiple feeding is detected in the course of stacking the bundle of notes 68′ or one or more of the notes are rejected for any reason, the bundle is not fed to the note exit slot 110. Instead the stripper plate assembly 96 is pivoted into a position as shown by the dashed outline 96′ and the belts 100, 102 are operated in the reverse direction to deposit the bundle 68′ into a reject note container 114 via an opening 116.
By rejecting bundles of notes at this late stage in the dispensing process, many notes may be deposited in the reject note container (e.g. where 50 notes are being dispensed and the 50th note is rejected, 49 “good” notes are deposited in the reject note container. This increases the transaction time for a user, results in the reject note container becoming full quickly and decreases the number of wasted “good” notes as these cannot now be dispensed.